Study of the tribologically transformed structure created during fretting tests

In fretting, without a lubricant, structures fail through wear involving debris. Various metallographic assessments show that this debris creation derives from a special structure, hereafter called the “tribologically transformed structure” (TTS). The latter is nucleated at the very beginning of a contactʹs life, and eventually masks the initial materialʹs tribological behaviour. This TTS is very hard and brittle, and is quickly destroyed, which explains why TTS is rather difficult to observe. This study focuses on initiation mechanisms which, up to now, are still highly controversial. Large amounts of TTS are observed after fretting tests, which is the reason why they were chosen as the means of investigation. In this paper, the various possible creation mechanisms for TTS will be analysed. From this overview, two nucleation models are chosen: one is based on “mechanical alloying” considerations, and the other is linked to high-strain-recrystallisation phenomena. Transmission electron microscopy (TEM) investigations are used to check these assumptions.